The present invention relates generally to an apparatus for braking elevator cars and, in particular, to an apparatus for controlling retardation forces during emergency braking.
An elevator car braking apparatus with two scissors-like frame members, at which a wedge-shaped friction member and a brake block are arranged at one end and a compression spring and an electromagnet are arranged at the other end, is shown in the German patent DE-A1 3 934 492. In case of an emergency, the wedge-shaped friction member is moved upwardly by a device so that a friction force initiated by the brake block on a guide rail slows down and stops the downwardly moving elevator car. The slowing-down of the elevator car is measured by means of an acceleration-measuring sensor. A feedback regulator feeding the brake electromagnet is controlled on the basis of the data supplied by the measuring sensor such that the friction force between the guide rail and the brake block maintains a constant slowing-down of the elevator car.
A disadvantage of the above described braking apparatus is that much space is required for the scissors-like braking equipment, which in turn makes the arrangement of the guide equipment of the elevator car more difficult. A further disadvantage lies in the triggering device which is formed by a lever and the wedge-shaped friction member and which, in particular at the beginning of the slowing-down, causes uncontrollable peak retardation of the elevator car.